1. Field of the Invention
The present invention relates generally to magnetic devices, and more specifically, the present invention relates to components that transfer energy in power converters. It involves a method of construction that reduces the cost of inductors and transformers that have more than one winding.
2. Background Information
Most modern electronic equipment requires a regulated source of direct current (DC) voltage to operate. The magnitude of the regulated voltage is typically less than 20 volts. Often the regulated DC voltage must be obtained from an unregulated source of DC or alternating (AC) voltage that has a magnitude several times greater than the desired regulated value. It is the purpose of electronic power supplies to provide the regulated voltage from the unregulated source.
Typical power supplies commonly utilize an energy transfer element to change the magnitude of one voltage or current to a different voltage or current.
FIG. 1 shows an example of a common construction for an energy transfer element. As shown, the energy transfer element includes a magnetic element 100, a primary winding 101 that forms a primary port P1, and a secondary winding 102 that forms a secondary port S1. The two-dimensional drawing in FIG. 1 shows that the structure of the magnetic element 100 is a toroid.
The important characteristic of the toroidal structure is that the magnetic element defines a closed structure with a hole such that the magnetic element completely surrounds every turn of every winding. As a consequence of this closed construction, one end of each of the windings 101 and 102 must be threaded or pass through the hole defined by the inner diameter 103 of the circular structure. This restriction complicates the manufacturing process. Manufacturing becomes increasingly difficult and more costly as the inner diameter 103 gets smaller. The curvature of the circular hole in magnetic element 100 is an additional complication to the application of windings.
FIG. 2 is a modification to the toroidal structure of the magnetic element 100 in FIG. 1. The structure of the magnetic element 200 in FIG. 2 is a closed construction like magnetic element 100. The major difference between magnetic element 200 and magnetic element 100 is that the hole in magnetic element 200 is formed from sections that are defined by straight lines, whereas the geometry about the hole of magnetic element 100 is curved. The closed rectangular structure of magnetic element 200 has the same fundamental problems with manufacturability and high cost as the closed circular structure of magnetic element 100. One end of windings 201 and 202 must be threaded or pass through the inner rectangular area 203.
The problem of manufacturability is generally addressed by the technique illustrated in FIG. 3. The closed structure of the magnet element 200 of FIG. 2 has been separated into the two pieces 300 and 301 having open structures in FIG. 3. Additionally, two tubes 302 and 303 of a rigid nonmagnetic material that is also an electrical insulator are introduced to hold the windings 304 and 305. One familiar with the construction of magnetic components for power converters will recognize 302 and 303 as bobbins. A bobbin is a rigid structure of an electrically insulating nonmagnetic material that holds windings for a magnetic element, to provide mechanical support and to maintain the relative positions of the windings when the magnetic element is absent. One familiar with bobbins for magnetic elements will know that bobbins typically contain conductive pins that terminate the ends of the windings, but are not necessary to realize the main advantages of the technique illustrated in FIG. 3.
The technique of constructing a magnetic device that has a closed structure from multiple elements that have open structures, shown by example in FIG. 3, removes the restriction that requires the ends of the windings to pass through an opening in a closed structure such as those in FIG. 1 and FIG. 2. However, this benefit to manufacturing is often defeated by the additional cost of the bobbins.